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I want to investigate the maximum possible parallelism of quantum operations on a specific IBM device (such as the latest heavy-hex architecture), which requires a basic knowledge of their control electronics. I want to know whether individual qubits have their independent control units or share the same control unit, and how the related control constraints restrict the concurrency of quantum gates. I found some control related knowledges about flux-tuable transmon qubits. However, IBM devices are based on fixed-frequency qubits. Are there any relevant reference papers. Thanks a lot!

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From Demonstration of quantum volume 64 on a superconducting quantum computing system chapter IV on dynamical decoupling, we read:

When quantum circuits are mapped to physical hardware, not all physical gates can be performed simultaneously. Gate execution-times can vary significantly, not only between single- and two-qubit gates, but also between individual qubits and qubit-pairs. In addition, architecture-specific gate schemes and connectivity determine which and how many gates can be executed in parallel.

which suggests that the control units are not fully independent.

In Scalable quantum circuit and control for a superconducting surface code (though representing state as of 2016) we read:

Our eight-qubit unit cell uses three fixed frequencies for all single-qubit control and eight detuning sequences for two qubit gates. This approach to classical control allows significant control hardware savings via spatial multiplexing.

which appears to further suggest that some shared control wave generators may be used.

These are still only guesses though. Ultimately for information like this you have to reach out to IBM, as their architectures are proprietary, but they may be willing to share some information for research purposes.

Alternatively an option to get some insight would be to thoroughly check documentation and/or examples for Qiskit Metal, which could tell you something about design principles used.

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